Proceeding from a detailed study of the main features of the pattern of activity present in the antagonist during fast (ballistically initiated) movements, we are planning to define the role of several structures in shaping such pattern on the basis of sensory input data. To this end discrete lesions will be placed in the cerebellar cortex and nuclei of trained monkeys, as well as in other structures. Our interest is limited to permanent irreversible changes produced by such lesions. This program is designed to seek details concerning the logic whereby fast movements are automatically controlled on the basis of sensory input data.